It was much rumored as soon as the 5-4 decision that upheld President Obama's signature health care law was announced.

Chief Justice John Roberts had sided with the liberal wing of the court and he had done so after initially voting in favor of striking down the individual mandate, the part of the law the required every American to obtain health care.

CBS News' Jan Crawford has a scoop today in which she talks to unnamed insiders. They tell her that Roberts first agreed that the individual mandate was unconstitutional and assigned himself the task of writing the majority opinion. During the course of that writing, Roberts changed his mind. Instead, he decided, the individual mandate was constitutional under the taxation power of Congress.

That unleashed feverish negotiations between the chief justice and Justice Anthony Kennedy, the expected swing vote on the case.

Crawford's full piece is worth a read. But here are important graphs:

"It is not known why Roberts changed his view on the mandate and decided to uphold the law. At least one conservative justice tried to get him to explain it, but was unsatisfied with the response, according to a source with knowledge of the conversation.

"Some informed observers outside the court flatly reject the idea that Roberts buckled to liberal pressure, or was stared down by the president. They instead believe that Roberts realized the historical consequences of a ruling striking down the landmark health care law. There was no doctrinal background for the Court to fall back on - nothing in prior Supreme Court cases - to say the individual mandate crossed a constitutional line.

"The case raised entirely new issues of power. Never before had Congress tried to force Americans to buy a private product; as a result, never before had the court ruled Congress lacked that power. It was completely uncharted waters."

Last week, The New York Times tried to explain Roberts' thinking. The analysis piece by Adam Liptak is worth a read. Liptak argues that this decision by Roberts wasn't at all a shift in posture. Roberts very often refers to Justice Oliver Wendell Holmes Jr.

"In the earlier cases, Chief Justice Roberts had drawn varying lessons from Justice Holmes's observation about the grave and delicate duty the Constitution imposes on the Supreme Court," the Times reports. "Once, he said it counseled caution. Another time, he said it required action. On Thursday, he chose compromise, or perhaps statesmanship."